When the time comes to install Slackware on your computer, you have a limited number of options regarding the location of your Slackware packages. Either you install them from the (un)official Slackware CDROM or DVD, or you copy them to a pre-existing hard disk partition before starting the installation procedure, or else you fetch the packages from a NFS server.

The number of possible options for booting your Slackware installer is similarly limited: either you boot your computer from the bootable first CDROM of the Slackware CD set, or from the DVD, or (in those cases where the computer BIOS refuses to recognize the CD as bootable) create boot/root floppies and boot from those. There is even loadlin, the DOS based Linux starter, but let's not concern ourselves with the past today.

But what if your PC is lacking a floppy drive - or even a CDROM drive? Brands of PC's are on the market today (ultra-portable laptops for instance) that are unable to install Slackware the traditional way. However, these machines are commonly equipped with network peripherals, like bluetooth, wireless and wired network cards. How to solve this dilemma? Buy an external CD drive?

Well, there is one way of booting your computer that the Slackware installer does not yet support. That is the network boot. Network boot, or “PXE boot”, requires support from your computer's network card and BIOS. Also, instead of installing packages from a Slackware CDROM set, you will need a network server that can instruct your computer how to fetch those packages from the network.

In this article, I want to present a way of installation that uses the network as the carrier medium, with a server on the local network that holds the boot kernel and the root filesystem (which contains the setup program), and also has all the Slackware packages. This means, there is no need for a floppy or CDROM drive.
Be warned: setting it all up is not trivial, and you need more than a beginner's level of Linux knowledge, but this text and the accompanying example scripts in the last section should get you up and running even if you do not completely understand what is going on

I will describe how to setup a server with the proper software, and how to modify some of the files on the Slackware CDROM so that PXE-boot becomes a supported installation method for Slackware Linux.

The commonly used method of booting a computer over the network is called PXE or Preboot Execution Environment. If you want your computer to boot using PXE, it needs a network card with PXE-capable firmware, and a BIOS that supports network boot. Most modern network cards (and computers) sold on the market today support this. When a computer boots from the network , it is the network card that downloads the bootloader, kernel and a filesystem - any Operating System that might already be installed on the computer will be untouched.
You can just as well boot a diskless computer using PXE - in fact this is how Thin Clients and the Linux Terminal Server Project work.

Of course, the other end of the network needs our attention, too. A PXE server needs to be available on the local network. The PXE firmware in your computer's network card will contact this server in order to fetch some kind of bootable program code and bootstrap itself. What happens after the computer boots has no longer anything to do with the PXE boot stage, it is the bootstrapping process we're interested in.

We will cover the requirements for such a server in one of the next paragraphs.

The Slackware network installation process will roughly be as follows:

You start the computer that is going to receive Slackware;

On startup, you make sure you select network boot in the BIOS startup - either by activating a custom startup sequence, by entering a boot menu by pressing a function key like F12, or else by preselecting network boot as first option in the BIOS.

When the computer boots, the network card activates its PXE code and tries to contact a PXE server. When such a server exists on the LAN, it will tell the card where to download a piece of bootable code, an Operating System kernel (the Slackware Linux kernel) and an initial ramdisk (aka initrd - the compressed root-filesystem image where the setup program, libraries and kernel modules are stored). You will see a page full of mumbo-jumbo as the card broadcasts on the LAN, and probes for possible candidate configurations to download;

If a willing PXE server was found, your computer's network card will then download a kernel and initrd, boot the Linux kernel, unpack the initrd into a ramdisk and start the Slackware installer's initialization sequence. This is where you'll be in familiar territory again, since this is exactly what happens if you had booted from a CDROM or a floppy. But the fun is not over…

Since we booted the computer using code that did not originate from our computer, we will have to fetch the remainder of the data - the Slackware packages - from the network as well. It's just that the freshly booted Linux kernel has no idea how it came to be running on the computer: you will have to initialize the network all over again. The network card's PXE firmware has done it's job and is no longer in the picture. So:

We need to load a kernel driver for our network card and locate a NFS server that holds the Slackware package tree. Currently, NFS is our only means of getting to network data at all. Before starting cfdisk and setup, we need to run the (pcmcia and/or) network command to probe the network card and load a suitable driver. If your network card is not supported by any of the available drivers, you're out of luck and will have to re-evaluate your options.

From here on, installation proceeds as usual, under the condition that you select NFS server as the source of the Slackware packages.

This is the interesting part (well in my opinion at least - many people consider this as a dark art).
A PXE Server is really a mix of several components. We need

A service that understands the BOOTP protocol. BOOTP is a network protocol somewhat like DHCP, and it is used by the PXE firmware to broadcast on the network its desire to find a suitable server to download the bootstrap code from. The ISC DHCP Server which comes as part of Slackware fulfills this requirement, since it supports BOOTP as well as DHCP.

A download service for the bootstrap code. A TFTP (trivial file transfer protocol) server is needed for this. Slackware ships with an implementation of a TFTP server called tftpd-hpa which does what we need.

And for the Slackware installer, a NFS server is required because we must perform a network install. Slackware does not know the concept of installation from a ftp server (yet?). We can use Slackware's stock NFS server for that.

We'll look at how to set up the DHCP, TFTP and NFS services on a Slackware computer so that they work together as a PXE server.

For ease of instruction, I will make a number of assumptions. These assumptions are reflected in IP addresses and address ranges that I use in my examples, in the names of directories, computers and network domains. This means that if you use the examples in this article, you should make certain that you replace all occurrences of these specifics with values that apply to your own network.

Our example network uses IP addresses in the range of 192.168.0.0 to 192.168.0.254. This is equivalent to a network range 192.168.0.0/24 or 192.168.0.0/255.255.255.0.

Our network server will have the IP address of 192.168.0.1 and the default gateway is 192.168.0.10. Server and gateway can be (but do not need to be) the same physical machine.

The IP address range that the DHCP server will use to lease to DHCP/BOOTP enabled computers is 192.168.0.50 to 192.168.0.100.

The DNS domain will be “my.lan”.

The server will run all required services, i.e. acts as the LAN's DNS,DHCP, TFTP and NFS server. If you decide to separate DHCP and TFTP services onto two different servers (it does not matter where the NFS server runs), I will add a comment on what you should take care of in the DHCP section that comes next.

Directories are used as follows:

Toplevel of the complete Slackware 11.0 directory tree (excluding the source code if you're short on disk space) is /mirror/Slackware/slackware-11.0

The directory where we store the boot files for the TFTP server is /tftpboot/slackware-11.0

You probably already have a DHCP server running on your network. You can try and modify it's configuration so that it will do want we want, or if that is impossible (for instance because the DHCP server is running on your DSL/Cable router) you could consider disabling that and setting up a Slackware DHCP server for your LAN with much enhanced functionality.

Slackware includes the ISC DHCP server package (dhcpd). Two example /etc/dhcpd.conf configuration files for this DHCP Server are included in the last section of the article.

If you don't want to be bothered with fancy configurations but want a quick solution that will just work for your network, use the first (simple) example/etc/dhcpd.conf configuration file as well as the provided /etc/rc.d/rc.dhcpdstart script and you'll be up and running in minutes. It requires no editing of files, the examples will work out of the box.

If you know what you're doing and understand (more or less) how the DHCP server works, you can have a look at the second, more complex, /etc/dhcpd.conf example which has more features and offers control over what computers are allowed to do a network boot.
The rest of this chapter deals with the setup of a complexDHCP configuration.

By default, we should no allow network boots in our network (which is safer of course - imagine a computer that does an un-intended network boot and suddenly finds itself running the Slackware installer!). In the /etc/dhcpd.conf configuration file, we add a group section were we can add those computers that we allow as network boot clients; the typical host statement for a computer looks like this

Nothing spectacular; a computer is defined by the network card's hardware address (MAC address) and we let the DHCP Server always assign it the same IP address. The boot-specific parameters are all contained in the group block and look like this:

This makes the DHCP server recognize network boot clients that use PXE and serves them the PXElinux boot loader /slackware-11.0/pxelinux.0. What this boot loader does will be explained further down the article.

The next-server parameter contains the IP adddress of the TFTP server. This will often be identical to the DHCP server's IP address, but if you have a TFTP server that is running on a different IP address than the DHCP server (i.e. they run on separate servers) you will have to add the remote IP address instead, like this (assuming the TFTP server is running on IP address 192.168.0.254):

next-server 192.168.0.254;

If you are running a version of ISC dhcpd that is >= 3.0.3 , then the addition of a next-server <ipaddress>; line is mandatory. For older releases this was only needed if the TFTP and DHCP Servers actually had different addresses.
If you fail to set the next-server address, the siaddr field in the data returned to the client is set to zero where in the past it would default to the DHCP server's own IP address (which often happened to be the IP address of the TFTP server as well). The PXE client uses the siaddr field to determine the IP address of the TFTP server and so the PXE booting will stall at the point of looking for a TFTP server.

If you are already using dnsmasq as your DNS/DHCP server, then the above instructions for the ISC DHCP server are not applicable to your setup. In that case, I have another Wiki article (which focuses on QEMU) for you where I have documented the required modifications to the dnsmasq server.

We need to create the directory /tftpboot which will hold the bootstrap files that tftpd will serve:

mkdir /tftpboot

This directory is the root of a secure jail (the -s /tftpboot parameter in /etc/inetd.conf).
The tftpd service is now configured and running. We just need to populate it's root directory, but I'll keep that for another paragraph.

You need to export the directory where you keep your local copy of the Slackware packages, for instance by adding this to /etc/exports:

/mirror/Slackware 192.168.0.0/24(ro,sync,insecure,all_squash)

in case your Slackware packages are located somewhere below /mirror/Slackware (like in our example network). The above line makes this directory tree available (read-only) to NFS clients in the local network defined by the IP address range 192.168.0.0/24.

If you had to add this to the /etc/exports file, you will need to restart the NFS server:

/etc/rc.d/rc.nfsd restart

For simplicity's sake: these are the steps if you just want this working and have no prior experience with NFS nor have such a server running at the moment (remember that pathnames/IP addresses are used that apply to our example network - adjust as needed):

Create a file named /etc/exports with the following content:

/mirror/Slackware 192.168.0.0/24(ro,sync,insecure,all_squash)

Use the directory mentioned in /etc/exports to copy (or move) the contents of your Slackware files to: The directory /mirror/Slackware/slackware-11.0 should be the root of the Slackware tree, containing such files as the ChangeLog.txt and subdirectories like slackware and kernels.

Make the NFS server startup script executable so that the NFS server will start on every boot:

PXELinux is much like isolinux, which is the bootloader that is used for the bootable Slackware CDROM #1. In fact, both programs are written by the same author and are available in Slackware via the syslinux package.
We will start with the configuration file isolinux.cfg and the root disk image initrd.img that are used to create the Slackware CDROM and modify those so they can be used with a pxelinux bootloader.

As you can see in the DHCP section, the DHCP server offers any interested PXE client (i.e. your computer's network card) the file /slackware-11.0/pxelinux.0 - this file contains the bootable code that subsequently downloads and starts a Linux kernel, and downloads and extracts the root filesystem containing the setup program and everything else that we need.
This filename /slackware-11.0/pxelinux.0 indicates a pathname relative to the root of the TFTP server. The PXE client will use the tftp protocol to fetch this bootloader. So this is what we do: create this directory slackware-11.0 and copy the required files into it. First, the pxelinux bootloader itself:

Also, we need the files from the Slackware CDROM that show the informative messages in the beginning. Assuming your mirror of the Slackware release can be found in /mirror/Slackware/slackware-11.0/ (change paths in the below commands if your location is different) :

The usual way of installing Slackware from a NFS server repository, is to boot the Slackware CDROM, and run (pcmcia and) network to load all the drivers for your network card before starting setup to commence the installation procedure. When you type pcmcia and/or network, the Slackware installer will look for the appropriate driver files on an available CDROM, and if no CDROM is found it prompts you to insert floppy disks.
Now, with a boot from the network we are assuming there is no CDROM and no floppy drive available to us. So, we need to add all the drivers we need to the root filesystem that the PXElinux bootloader downloads from the TFTP server (contained in the initrd.img file).

This is the basic procedure - we will carry this out on the server. I still assume your local mirror of the Slackware release can be found under /mirror/Slackware on your server:

Create a staging area where we do all our nifty work:

mkdir -p /tmp/pxe

Extract the image containing the root filesystem from the compressed file initrd.img:

You've probably noticed I mount these images read-only; we're only going to copy files out of them.

Use the dd command to create a new file of sufficient size (called newinitrd). At the end of the process this file will contain a filesystem which holds the combined contents of the Slackware disk images we just loop-mounted.
With “sufficient” I mean the size must be at least the combined sizes of the uncompressed disk images we are going to copy into our new filesystem. In my example dd command below I use a number of 9500 1kB sized blocks which amounts to a 9.5MB file:

dd if=/dev/zero of=/tmp/pxe/newinitrd bs=1k count=9500

How did I get at that number 9500? Well, you sum the sizes of the initrd.dsk, network.dsk and pcmcia.dsk files and make sure you use a number that is not smaller than that sum. The following command is the geek way to return the sum value:

We then create a filesystem inside this file (and use the -F flag to mkfs.ext2 to indicate that we are fully aware we're applying the command to a non-block device). Also, tune the filesystem so that it will never ever ask for a filesystem check (fsck) when it gets mounted:

mkfs.ext2 -m 0 -F /tmp/pxe/newinitrd
tune2fs -i 0 /tmp/pxe/newinitrd

Now that we have a usable filesystem, loop-mount this file as well (this one read/write!):

mkdir -p /tmp/pxe/out/
mount -o loop /tmp/pxe/newinitrd /tmp/pxe/out/

Copy the contents of the three Slackware disk images into the still empty new file:

Modify the scripts that are executed when you type pcmcia and network so that they do no longer look for CDROM or floppies to mount the disk images from - because all the required stuff will now be available in the new root filesystem:

Note you can not gzip the image file correctly as long as it is still mounted!

And finally, clean up behind us:

rm -r /tmp/pxe

I have written a script create_slackboots.sh that does all of this fully automatically (and more!), and you can download it at http://www.slackware.com/~alien/tools/slackboot/. Do not forget to also download the other files that you'll find at that URL, because the script needs those to patch the pcmcia and network scripts. Be aware that this script also adds the content of network26.dsk (the network drivers for the huge26.s kernel) to our big new initrd.img, which is something I omitted from the detailed steps above in order to keep the story readable

You can also just download a ready-made initrd.img of course.
I have an accompanying pxelinux configuration file too. If you rather want to create that file yourself, use the aforementioned create_slackboots.sh script or read the next paragraph.

and edit the resulting file so that every occurrence of the absolute path name /kernels will be replaced with the relative pathname kernels, and the size of the ramdisk is increased to the amount where our bigger root filesystem will still fit. Rule of thumb: since we added the contents of the pcmcia.dsk and the network.dsk filesystems to the initrd.img, we need a ramdisk that is roughly 3MB larger than is used for CDROM-booting. I assume 9.5 MB will do (this should be at least equal to the size of the uncompressed file newinitrd we created in the previous section):

You now have a fully configured PXE server. Try it out!
Take a computer that is able to do a network boot, start it, and watch it go through the motions of contacting the PXE server, downloading the PXE boot code and presenting you with the familiar Slackware installation screen! From there on you're on familiar grounds: choose a kernel, and off you go.

If you're not familiar with NFS installations, here are some hints:

After you log in as root and setup the partitions using fdisk or cfdisk, you must load a kernel module for your network card.
This probably will not be a PCMCIA card (I don't know of any that can perform a PXE boot), so it won't be necessary running ”pcmcia” to load support for a PCMCIA card.
You do have to run the command ”network” which is the interactive program that allows you to pick a driver or let Slackware probe the card and load the correct driver. If the network program fails to detect the card, and you know what driver your card needs but don't see it listed, you're out of luck!

Select a “NFS installation” once you get to the “SOURCE” dialog. You will need to supply a couple of values for IP Addresses and the NFS server directory. These are:

Your own IP Address (pick any unused)

192.168.0.111

Your netmask

255.255.255.0

The gateway

192.168.0.10

NFS server address

192.168.0.1

Slackware directory on the NFS server

/mirror/Slackware/slackware-11.0/slackware

From this point onwards, the installation proceeds just as when the SOURCE would have been a CDROM.

A more advanced /etc/dhcpd.conf file for your DHCP server where you can specify exactly which computers are allowed to boot from the network using PXE (but you will have to collect their MAC addresses yourself and put them into separate host{} entries):